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IOSTAT(1)                              Linux User's Manual                              IOSTAT(1)



NAME
       iostat  -  Report Central Processing Unit (CPU) statistics and input/output statistics for
       devices and partitions.

SYNOPSIS
       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [  -j  {
       ID | LABEL | PATH | UUID | ... } ] [ [ -T ] -g group_name ] [ -p [ device [,...] | ALL ] ]
       [ device [...] | ALL ] [ interval [ count ] ]

DESCRIPTION
       The iostat command is used for monitoring system input/output device loading by  observing
       the  time  the  devices are active in relation to their average transfer rates. The iostat
       command generates reports that can be used to change system configuration to  better  bal-
       ance the input/output load between physical disks.

       The  first  report generated by the iostat command provides statistics concerning the time
       since the system was booted, unless the -y option is used (in this case, this first report
       is  omitted).   Each subsequent report covers the time since the previous report. All sta-
       tistics are reported each time the iostat command is run. The report  consists  of  a  CPU
       header  row followed by a row of CPU statistics. On multiprocessor systems, CPU statistics
       are calculated system-wide as averages among all processors. A device header row  is  dis-
       played followed by a line of statistics for each device that is configured.

       The  interval  parameter  specifies the amount of time in seconds between each report. The
       first report contains statistics for the time since system startup (boot), unless  the  -y
       option  is  used  (in this case, this report is omitted).  Each subsequent report contains
       statistics collected during the interval since the previous report.  The  count  parameter
       can  be  specified  in  conjunction with the interval parameter. If the count parameter is
       specified, the value of count determines the number of reports generated at interval  sec-
       onds apart. If the interval parameter is specified without the count parameter, the iostat
       command generates reports continuously.


REPORTS
       The iostat command generates two types of reports, the  CPU  Utilization  report  and  the
       Device Utilization report.

       CPU Utilization Report
              The first report generated by the iostat command is the CPU Utilization Report. For
              multiprocessor systems, the CPU values are global averages  among  all  processors.
              The report has the following format:

              %user
                     Show  the percentage of CPU utilization that occurred while executing at the
                     user level (application).

              %nice
                     Show the percentage of CPU utilization that occurred while executing at  the
                     user level with nice priority.

              %system
                     Show  the percentage of CPU utilization that occurred while executing at the
                     system level (kernel).

              %iowait
                     Show the percentage of time that the CPU or CPUs were idle during which  the
                     system had an outstanding disk I/O request.

              %steal
                     Show  the percentage of time spent in involuntary wait by the virtual CPU or
                     CPUs while the hypervisor was servicing another virtual processor.

              %idle
                     Show the percentage of time that the CPU or CPUs were idle  and  the  system
                     did not have an outstanding disk I/O request.

       Device Utilization Report
              The second report generated by the iostat command is the Device Utilization Report.
              The device report provides statistics on a per physical device or partition  basis.
              Block  devices  and  partitions  for  which  statistics  are to be displayed may be
              entered on the command line.  If no device nor partition is entered,  then  statis-
              tics are displayed for every device used by the system, and providing that the ker-
              nel maintains statistics for it.  If the ALL keyword is given on the command  line,
              then  statistics  are  displayed  for every device defined by the system, including
              those that have never been used.  Transfer rates are shown in 1K blocks by default,
              unless  the  environment  variable  POSIXLY_CORRECT  is set, in which case 512-byte
              blocks are used.  The report may show the following fields, depending on the  flags
              used:

              Device:
                     This  column  gives  the  device  (or  partition) name as listed in the /dev
                     directory.

              tps
                     Indicate the number of transfers per second that were issued to the  device.
                     A transfer is an I/O request to the device. Multiple logical requests can be
                     combined into a single I/O request to the device. A transfer is of  indeter-
                     minate size.

              Blk_read/s (kB_read/s, MB_read/s)
                     Indicate  the  amount  of data read from the device expressed in a number of
                     blocks (kilobytes, megabytes) per second. Blocks are equivalent  to  sectors
                     and therefore have a size of 512 bytes.

              Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
                     Indicate  the  amount of data written to the device expressed in a number of
                     blocks (kilobytes, megabytes) per second.

              Blk_read (kB_read, MB_read)
                     The total number of blocks (kilobytes, megabytes) read.

              Blk_wrtn (kB_wrtn, MB_wrtn)
                     The total number of blocks (kilobytes, megabytes) written.

              rrqm/s
                     The number of read requests merged  per  second  that  were  queued  to  the
                     device.

              wrqm/s
                     The  number  of  write  requests  merged  per second that were queued to the
                     device.

              r/s
                     The number (after merges) of read requests  completed  per  second  for  the
                     device.

              w/s
                     The  number  (after  merges)  of write requests completed per second for the
                     device.

              rsec/s (rkB/s, rMB/s)
                     The number of sectors (kilobytes, megabytes) read from the device  per  sec-
                     ond.

              wsec/s (wkB/s, wMB/s)
                     The  number of sectors (kilobytes, megabytes) written to the device per sec-
                     ond.

              avgrq-sz
                     The average size (in sectors) of  the  requests  that  were  issued  to  the
                     device.

              avgqu-sz
                     The average queue length of the requests that were issued to the device.

              await
                     The  average time (in milliseconds) for I/O requests issued to the device to
                     be served. This includes the time spent by the requests  in  queue  and  the
                     time spent servicing them.

              r_await
                     The average time (in milliseconds) for read requests issued to the device to
                     be served. This includes the time spent by the requests  in  queue  and  the
                     time spent servicing them.

              w_await
                     The  average  time (in milliseconds) for write requests issued to the device
                     to be served. This includes the time spent by the requests in queue and  the
                     time spent servicing them.

              svctm
                     The average service time (in milliseconds) for I/O requests that were issued
                     to the device. Warning! Do not trust this field any more.  This  field  will
                     be removed in a future sysstat version.

              %util
                     Percentage  of  elapsed  time  during  which I/O requests were issued to the
                     device (bandwidth utilization for the device). Device saturation occurs when
                     this value is close to 100%.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -g group_name { device [...] | ALL }
              Display  statistics  for a group of devices.  The iostat command reports statistics
              for each individual device in the list then a line of  global  statistics  for  the
              group  displayed  as group_name and made up of all the devices in the list. The ALL
              keyword means that all the block devices defined by the system shall be included in
              the group.

       -h     Make the Device Utilization Report easier to read by a human.

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display  persistent  device  names. Options ID, LABEL, etc. specify the type of the
              persistent name. These options are not limited, only prerequisite is that directory
              with  required  persistent  names  is  present  in /dev/disk.  Optionally, multiple
              devices can be specified in the chosen persistent name  type.   Because  persistent
              device names are usually long, option -h is enabled implicitly with this option.

       -k     Display statistics in kilobytes per second.

       -m     Display statistics in megabytes per second.

       -N     Display  the  registered device mapper names for any device mapper devices.  Useful
              for viewing LVM2 statistics.

       -p [ { device [,...] | ALL } ]
              The -p option displays statistics for block devices and all their  partitions  that
              are used by the system.  If a device name is entered on the command line, then sta-
              tistics for it and all its partitions are displayed. Last, the  ALL  keyword  indi-
              cates that statistics have to be displayed for all the block devices and partitions
              defined by the system, including those that have never been used. If option  -j  is
              defined  before  this  option, devices entered on the command line can be specified
              with the chosen persistent name type.

       -T     This option must be used with option -g and indicates that only  global  statistics
              for the group are to be displayed, and not statistics for individual devices in the
              group.

       -t     Print the time for each report displayed. The timestamp format may  depend  on  the
              value of the S_TIME_FORMAT environment variable (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -y     Omit first report with statistics since system boot, if displaying multiple records
              at given interval.

       -z     Tell iostat to omit output for any devices for which there was no  activity  during
              the sample period.


ENVIRONMENT
       The iostat command takes into account the following environment variables:


       S_TIME_FORMAT
              If  this  variable  exists  and  its  value  is ISO then the current locale will be
              ignored when printing the date in the report header. The iostat  command  will  use
              the  ISO  8601 format (YYYY-MM-DD) instead.  The timestamp displayed with option -t
              will also be compliant with ISO 8601 format.


       POSIXLY_CORRECT
              When this variable is set, transfer rates are shown in 512-byte blocks  instead  of
              the default 1K blocks.


EXAMPLES
       iostat
              Display a single history since boot report for all CPU and Devices.

       iostat -d 2
              Display a continuous device report at two second intervals.

       iostat -d 2 6
              Display six reports at two second intervals for all devices.

       iostat -x sda sdb 2 6
              Display  six reports of extended statistics at two second intervals for devices sda
              and sdb.

       iostat -p sda 2 6
              Display six reports at two second intervals for device sda and all  its  partitions
              (sda1, etc.)

BUGS
       /proc filesystem must be mounted for iostat to work.

       Kernels older than 2.6.x are no longer supported.

       The  average  service  time  (svctm field) value is meaningless, as I/O statistics are now
       calculated at block level, and we don't know when the disk  driver  starts  to  process  a
       request. For this reason, this field will be removed in a future sysstat version.

FILES
       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

       /proc/diskstats contains disks statistics.

       /sys contains statistics for block devices.

       /proc/self/mountstats contains statistics for network filesystems.

       /dev/disk contains persistent device names.

AUTHOR
       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO
       sar(1), pidstat(1), mpstat(1), vmstat(8), nfsiostat(1), cifsiostat(1)

       http://pagesperso-orange.fr/sebastien.godard/



Linux                                     NOVEMBER 2012                                 IOSTAT(1)

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